1. Technical Field
The present invention relates to heating systems with fuel treatment means for liberating gas from solid fuel and in particular to a controlled system and method for clean-emission variable biomass gasification and combustion.
2. Description of the Prior Art
Biomass waste provides an abundant source of fuel from what might otherwise be considered waste. In addition, the plant matter from which the biomass waste comes is a renewable resource. As long as trees and other plants are harvested ecologically they keep replacing themselves with new growth by the natural growth cycle in many forests or by replanting. In addition, using plant growth as fuel maintains the natural carbon cycle in a 100% balanced state, because the clean gasification and combustion of biomass fuel puts back into the environment the same amount of carbon that occurs in the natural decay of plants. The carbon is then taken in by the living plants. However, burning coal, oil and natural gas creates a carbon overload in the environment from the centuries of stored carbon suddenly released into the environment.
Sources for biomass waste in the form of wood chips include whole tree chips from forestry maintenance including tree tops and waste in forests, brush and tree cuttings from parks and roadways, lumber mill waste, woodworking waste, crushed palletts, and any other sources of disgarded wood or wood byproducts. Many other sources of biomass waste exist in other forms from landfill sites, municipal waste collection, waste from companies using plant matter in any form, paper waste, and many other sources. The community itself can become the source of fuel for the community's own plants burning biomass fuel.
The major problem with biomass fuel is the substantial creosote and smoke discharge normally associated with wood burning and biomass burning stoves and furnaces which burn at relatively low temperatures at low efficiency rates. As well as a pollution problem, this is a great waste or resources, because the "pollutants" given off by such stoves and furnaces are hydrocarbon gases and particulates which will all burn cleanly if burned in an efficient high temperature system.
Most stoves, furnaces, and power plants using wood and biomass fuel are set up to burn somewhat efficiently, but only with specific qualities of fuels, typically limited in an allowable range of moisture content and other criteria such as phosphate content, which creates ash. Finding sources of biomass waste that meet specific requirements of moisture content and other criteria consistently is a major problem that further limits the efficiency of other systems, thereby wasting fuel and creating considerable pollution.
In other systems, such as large power plants, burning at relatively high temperatures in very large chambers "gasification" and burning of some of the hydrocarbon gases occurs spontaneously because of the high temperatures created from a huge fire source, the explosiveness of blown-in fuel and the fact that pyrolytic gases remain in some locations within the huge chambers to eventually burn up. Because these systems are relatively static and uncontrolled they are designed for a very limited range of fuel types and qualities and therefore burn less efficiently than they were designed for much of the time because of variations in fuel quality and changing climatic conditions such as air pressure, air temperature and humidity.
Smaller scale systems such as furnaces for buildings and stoves for homes are generally less efficient than the large power plants because they don't develop the same level of gasification spontaneously, because in smaller chambers the gases generally don't remain in the system as long, the same high temperature conditions are usually not attained, and fuel sources are even less uniform than municipal systems with rigid fuel requirements.
Although some systems have some controls built in to vary air input through flues or with some provision for creating gasification and combustion of the pyrolytic gases, most systems are relatively static with no feedback means to monitor the efficiency of the system; so they fail to control the gasification and pyrolytic gas combustion for variations in fuel quality and climatic conditions. Most biomass and wood burning systems require considerable time and labor in monitoring and manual adjustments to maintain some level of efficiency, especially systems requiring manual loading of fuel and unloading of ash.
Most other biomass fuel chambers are vertically oriented with vertical stacking of the fuel and vertical release and combustion of gases. The vertical system lacks control and creates inefficient, irregular, and incomplete gasification and combustion of pyrolytic gases, producing considerable pollution and waste as well as using more fuel to produce less heat.